The present invention relates to a surgical drill guide and locking bone plate that are demountably attachable to each other for retaining a precise alignment therebetween. More particularly, the present invention relates to a surgical drill guide assembly with a plurality of alignment drill tubes each having an expandable bushing that engages a fastener hole in a locking bone plate.
The use of surgical fixation plates for a variety of orthopedic applications is widely accepted. The plates are used by surgeons to mend, align, and alter compression of patient""s bones, and are typically fastened to the bones with a plurality of fasteners such as screws that are installed through holes in the plate. Proper orientation and alignment of fasteners and secure surgical fixation of the plates is crucial to avoiding future complications after implantation.
Locking bone plates used in spinal applications, such as those sold by SYNTHES Spine, must be installed with special care, as the plates are used for long term, intravertebral fixation, bone-fragment fixation, and anterior decompression in the cervical region of the spine. The margin for error in spinal surgery is quite small, particularly because of the sensitivity of the spinal cord and the risk inherent with invasive procedures around the spinal cord. In particular, the dimensions of vertebral bone available for setting fasteners are fairly constrained.
Each fixation plate hole should properly align with its associated screw so that each screw is seated correctly with the plate. Any misalignment of the screw within the plate hole risks tissue damage. In addition, improperly seated screws may result in an unstable or insecure connection of the plate to the bony material, thus potentially defeating the usefulness of the plate. Locking plates, in particular, demand precise fastener alignment. Typical cervical locking plates are generally about 2-3 mm thick, and include screw holes that are inclined by 9xc2x0 to 15xc2x0 with respect to the surface of the plate for optimal screw placement in the cervical region of the spine. A variety of types of bone screws are available for securing the plate to the desired anatomical site, such as the expansion-head screws disclosed in U.S. Pat. No. 4,484,570.
Known drill guides for locking plates, such as disclosed in U.S. Pat. No. 5,851,207, generally include a guide member for guiding a drill bit. A hollow collet is disposed coaxially with the guide member and has a radially expandable forward end with a neck. The neck is configured to press outwardly against an inner wall of a plate hole when the collet is in an expanded position, thereby securing the drill guide to the bone plate. An inconvenience associated with this drill guide is that it includes only one guide member, so the drill guide must be removed and reoriented within each bone plate hole for drilling successive holes in tissue.
The desirability of providing a drill guide that includes more than one guide tube has been recognized. For example, U.S. Pat. No. 5,180,388 discloses an applicator device with two guide tubes attached to a handle. A scale on the handle allows accurate determination of the movement of a drill inserted through the guide tubes and thus the depth of each hole. U.S. Pat. No. 4,714,469 shows another drill guide with an elongated arm having a distal end which is shaped to match the profile of a spinal implant for which the apparatus is to be used. Grooves in the drill guide are adapted to accommodate a drill bit, and linear markings are provided on the surface of the drill guide so that the correct depth for drilling is obtained. U.S. Pat. No. 5,112,336 shows a drill guide and template for use in orthopedic surgery, comprising a template and handle connected by a lockable universal joint. The template is provided with pins so that the template can be set into bone. The pins prevent the template from moving while bores are being made in the bone. Drill bores are provided in the template to conform to a selected prosthesis which the surgeon intends to implant. Despite these drill guide developments, none meets the demands of surgeons working with bone plates, as none attach to a bone plate.
U.S. Pat. No. 4,465,065 discloses an L-shaped surgical device for the connection of a fractured neck to the shaft of a femur by means of a pre-drilled connector plate. The tool has a grip and connector arm extending at right angles, and the tool and plate are interconnected by means of a long screw which passes through a longitudinal bore along the connector arm into a tapped hole in the top of the fixator plate. Two pins firmly attached to the connector arm also engage with corresponding holes in the upper part of the plate. Guide tubes extend through holes in the device to holes in the plate. The tool cannot be readily demountably attached to a plate, because the interconnection means are not quickly releasable.
U.S. Pat. No. 5,676,666 discloses a cervical plate holder/guide clamp that is a modified fixation forceps, and includes a handle, pivot joint, and blades. Each blade includes a guide head with opposing lips which attach to a plate. Guide cylinders are slidably positionable in each guide head and are pushed down to contact with the openings in the plate. The opposing lips contact the outer periphery of the plate.
U.S. Pat. No. 5,364,399 discloses an anterior cervical plating system. A drill and tap guide assembly is mounted on a fixation plate to provide a firm foundation for accurately drilling and tapping screw holes into the vertebra to be instrumented. The drill and tap guide assembly includes an assembly support which is engaged to the plate by way of a positioning screw and cross pins mounting the positioning screw to the guide body. A tap sleeve and drill guide can then be supported by the assembly support, which both thereby provide accurate positioning for a drill.
U.S. Pat. No. 5,423,826 discloses an anterior cervical plate holder/drill guide. The guide comprises two arms which pivot with respect to each other and a foot attached at the end of each arm. Each foot has a hook which is adapted to securely grasp a spinal plate and a pair of thru-holes. Each hole is aligned with a screw bore in a spinal plate when the guide assembly is engaged to the plate. A number of double-headed fixation pins hold the plate in position against the cervical spine during drilling and tapping. The hook on each foot of the guide attaches to a notch on each end of the plate.
The above-described patents disclose drill guides that do not engage the plate only within the plate fastener holes that receive the bone screws.
The invention relates to a surgical drill guide assembly comprising a pair of alignment drill tubes each configured to receive and guide a surgical drill bit; a pair of bushings configured to slidably receive the pair of alignment drill tubes, the bushings each having a radially expandable forward end configured to engage fastener holes in a bone plate; an actuation bar; a drill guide assembly handle coupled to the actuation bar; and a base coupled to the drill guide assembly handle. The alignment drill tubes are pivotably connected to the actuation bar. The bushings are configured and dimensioned to expand within the bone plate fastener holes to releasably lock the bushings to the bone plate, such that movement of the actuation bar toward the base urges the drill tubes into the bushings for expansion of the forward ends thus locking the bushings within the fastener holes of the bone plate. The bone plate may include at least two fastener holes.
Advantageously, the radially expandable forward end comprises a plurality of finger portions. The radially expandable forward end may be circular. Preferably, the radially expandable forward end comprises a shoulder, a neck, and an outwardly projecting rim disposed forward of the neck.
Each alignment drill tube has a drilling axis, and the drilling axes are coplanar and converge along a central plane forward of the radially expandable forward end of the bushings. In a preferred embodiment, each alignment drill tube is oriented at an angle of between about 5 and 22xc2x0 with respect to the central axis.
If desired, a latch can be included for releasably maintaining the actuation bar in an actuated position. When the expandable forward end of the bushing is circular shaped, and the fastener holes in the bone plate each have inner walls that define a circular shape, the expandable forward end is freely insertable and extractable from the bone plate fastener holes in a contracted position and engages the fastener holes when in an expanded position.
In additional embodiments of the assembly, the drill guide assembly handle is comprised of a grip pivotably connected to a handle member, and the grip is resiliently biased away from the handle member by leaf springs. Preferably, in a first position, the leaf springs maintain the grip and handle member in a spaced relation, with the bushings in non-expanded configurations and the alignment drill tubes in retracted positions. Application of a force to the grip and handle member counteracts the bias of the leaf springs and urges the grip and handle member to a second position, while moving the actuation bar toward the base, and urging the alignment drill tubes into the bushings for expansion of the forward ends.
The bone plate fastener holes may each have a wall thickness defined as the distance between a free-side surface and a bone-side surface of the bone plate. The radially expandable forward end of the bushing may comprise a shoulder, a neck, and an outwardly projecting rim disposed forward of the neck. The neck and rim together may span a length that is slightly longer than the thickness of the bone plate fastener hole wall, and the rim may abut the bone-side surface of the plate.